Method and kits for forming pontics in polymeric shell aligners

ABSTRACT

Systems and methods are disclosed for forming a pontic in a polymeric shell dental appliance, including providing a polymeric shell dental appliance of the type which is removably placeable over a patient&#39;s dentition, said shell having a concave trough which conforms to the teeth when the appliance is placed over the dentition and a location in the trough corresponding to a missing tooth; and depositing a flexible, durably affixed material in the location to form the pontic.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a division of U.S. application Ser. No.10/827,923 (Attorney Docket No. 018563-006110US/AT-00117.1), filed Apr.19, 2004, which was a division of U.S. patent application Ser. No.09/967,822 (Attorney Docket No. 018563-006100US/AT-00117), filed Sep.28, 2001, the full disclosure of which is incorporated herein byreference. This application is also related to U.S. application Ser. No.09/313,289 (Attorney Docket No. 018563-005200US/AT-00110) filed May 13,1999 (now U.S. Pat. No. 6318994); U.S. application Ser. No. 09/169,036(Attorney Docket No. 18563-004900US/AT-00106), filed Oct. 8, 1998 (nowU.S. Pat. No. 6,450,807); and U.S. application Ser. No. 09/169,034(Attorney Docket No. 018563-005000US/AT-00107), filed Oct. 8, 1998 (nowU.S. Pat. No. 6,471,511).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to orthodontics and more particularlyto methods and kits for for providing pontics in orthodontic appliances.

2. Description of the Background Art

Orthodontic treatments involve repositioning misaligned teeth andimproving bite configurations for improved cosmetic appearance anddental function. Repositioning teeth is accomplished by applyingcontrolled forces to the teeth over an extended period of time. This isconventionally accomplished by wearing what are commonly referred to as“braces.” Braces comprise a variety of appliances such as brackets,bands, archwires, ligatures, and O-rings. After they are bonded to theteeth, periodic meetings with the orthodontist are required to adjustthe braces. This involves installing different archwires havingdifferent force-inducing properties or by replacing or tighteningexisting ligatures. Between meetings, the patient may be required towear supplementary appliances, such as elastic bands or headgear, tosupply additional or extraoral forces.

Although conventional braces are effective, they are often a tedious andtime-consuming process requiring many visits to the orthodontist'soffice. Moreover, from a patient's perspective, they are unsightly anduncomfortable. Consequently, alternative orthodontic treatments havedeveloped. A particularly promising approach relies on the use ofelastic positioning appliances for realigning teeth. Such an appliancemay be comprised of a thin shell of elastic material, referred to as an“aligner” that generally conforms to a patient's teeth but is slightlyout of alignment with the initial tooth configuration. Placement of analigner over the teeth applies controlled forces in specific locationsto gradually move the teeth into the new configuration. Repetition ofthis process with successive appliances comprising new configurationseventually moves the teeth through a series of intermediate arrangementsto a final desired arrangement. A full description of an exemplaryelastic polymeric positioning appliance is described in U.S. Pat. No.5,975,893, and in published PCT application WO 98/58596 which designatesthe United States and which is assigned to the assignee of the presentinvention. Both documents are incorporated by reference for allpurposes.

Systems of preformed aligners employing technology described in U.S.Pat. No. 5,975,893, are commercially available from Align Technology,Inc., Santa Clara, Calif., under the tradename Invisalign® System. AlignTechnology, Inc., is the assignee of the present application. TheInvisalign® System relies on designing and fabricating the aligners tobe worn by the patient throughout treatment. The design of the alignersrelies on computer modeling of a series of successive tootharrangements, and the individual aligners are designed to be worn overthe teeth and to reposition the teeth to each of said tootharrangements. Usually, the set of aligners which is designed andfabricated at the outset of the treatment is able to successfullyreposition the teeth to a final desired arrangement.

With the Invisalign® System, as well as with other conventionalorthodontic treatment systems, it is sometimes necessary to extract oneor more teeth prior to tooth repositioning. At present, the Invisalign®System does not provide for filling in the space or void which remainswithin the aligner after the tooth is extracted with a structuralcomponent such as an artificial tooth which is commonly referred to as adental pontic.

The design and fabrication of dental pontics are described in U.S. Pat.Nos. 6,186,790; 6,050,820; 6,049,743 and 5,613,845, the full disclosuresof which are incorporated herein by reference. Currently, dentalprofessionals trained in the use of the Invisalign orthodontic systemare using a variety of materials and techniques known in the art tofabricate dental pontics which can be worn in the aligner extractionsite(s). The most commonly employed materials are tooth-shaded dentalcomposites typically used to repair carious lesions or fabricateprovisional (temporary) crowns and bridges. These materials consistmainly of a polymer matrix and dispersed reinforcing inorganic fillerparticles. Typical polymers used are based on dimethacrylate such asBis-GMA or urethane dimethacrylate (UDMA). Quartz, lithium aluminumsilicate and barium, strontium, or zinc glasses have been commerciallydistributed as fillers. Typically these materials are packaged as atwo-paste (base/catalyst) system. The polymer matrix may be visiblelight curable, self- curing, dual curing, and vacuum, heat and pressurecurable compositions as well as any combination thereof. A popularmethod for mixing and dispensing these materials involves the use of anautomix system whereby a dispensing gun is utilized to dispense the baseand catalyst, which are in separate cartridges, through a mixing cannuladirectly into the extraction site. Commercial examples of theautopolymerizing composites are Luxatemp Plus (DMG/Zenith), Integrity(Dentsply/Caulk), Protemp Garant (ESPE) and Turbo Temp (DanvilleEngineering). Alternatively light cured composites may be used tofabricate dental pontics. Commercial examples of light cured compositesare Revolution (Kerr), Star-Flow (Danville Engineering), and Tetric(Vivadent). Other useful dental composite materials are based on themethyl methacrylate polymer. Such acrylic polymers are well known andcommercially available for example as Jet Tooth Shade self-curingacrylic resin by Lang Dental.

Although dental composites have been used to fabricate dental ponticsfor the Invisalign system there remain two important disadvantages tousing these materials. First the ability of these materials to bond tothe aligner thermoplastic is poor and second these materials are verystiff and non-flexing. These characteristics significantly compromiseretention of the pontic in the aligner especially if it is subjected totorsional or flexing forces such as when the aligner is either beinginserted or removed from a patient's mouth or while the patient iscleaning their aligner using a cleaning device such a toothbrush ordenture brush.

While it has been proposed to paint or color a portion of the alignerwhich overlies the void (see co-pending application Ser. No. 09/454,278,the full disclosure of which is incorporated herein by reference),partial coloring of the aligner can affect the light transmittingproperties and be unaesthetic and the lack of any underlying structurecan weaken or lessen the resilience of the aligner and limit itseffectiveness.

For these reasons, it would be desirable to provide methods, systems,and kits for modifying an aligner to accommodate patients who have hadteeth extracted prior to treatment with an aligner or other polymericshell orthodontic appliance. It would be particularly desirable if themethods would permit an orthodontist or other clinician to modify analigner or other orthodontic appliance in the professional office,rather than having the modification done at the time of fabrication orat an off-site location. It would be further desirable still if thealigner could be modified by the treating clinician, fitted with thepatient, and further modified if necessary for patient comfort or otherreasons. The resulting modified aligners or other orthodontic appliancesshould be esthetically pleasing, and preferably should mask the absenceof an underlying tooth while the aligner or other appliance is worn. Atleast some of these objectives will be achieved by the inventionsdescribed hereinafter.

U.S. Pat. No. 5,975,893, and published PCT application WO98/58596, havebeen described above. Co-pending application Ser. No. 09/454,278, whichhas been published as WO99/028,228, relates to the fabrication ofaligners which have been colored to cover a void left where teeth havebeen removed. The full disclosures of each of these patents and pendingapplications are incorporated herein by reference.

SUMMARY OF THE INVENTION

The present invention provides methods and kits for forming a pontic ina polymeric shell dental appliance, such as the Invisalign® Systemaligners described above. In addition, the present invention providesfor methods of using such modified aligners for treating patients havinggaps between adjacent teeth, where the gaps resulted from prior toothextractions or other causes. In addition to the esthetic improvement,i.e., the voids or empty spaces between teeth will be generallyinvisible, it is believed that the pontics may reduce the tendency ofteeth to collapse inward toward each other as the teeth are moved toclose the gaps during the orthodontic treatment. In the case of theInvisalign® System, successive aligners which are used to treat anindividual patient can each be separately modified, with the ponticplaced in a gap between adjacent teeth being reduced in size as thetreatment progresses and the gap is gradually closed.

According to a first aspect of the present invention, a method forforming a pontic in a polymeric shell dental appliance, such as anInvisalign® System aligner, comprises providing a polymeric shell dentalappliance of the type which is removably placeable over a patient'sdentition. The shell will have a concave trough or cavity which conformsto the teeth when the appliance is placed or worn over the dentition.When the polymeric shell is worn, the treating clinician can determinethe location in the appliance trough where a tooth is missing. Thetreating clinician will usually note the location on the appliance andfurther determine the width and shape of the gap between the teeth.Optionally, in the case of the Invisalign® System aligners, the alignerwill have been shaped or otherwise modified to indicate the locationwhere the gap will occur. If not, the treating clinician can simply markthe aligner or take other appropriate steps to determine the location ofthe space within the trough.

After the space (or spaces) is determined, the pontic is formed byfilling the spaces(s) within the trough with a material that resembles atooth. While it would be possible to shape a cured material into thedesired geometry to be placed within the appliance trough, it will bemuch more convenient to fill the location with a relatively viscous butflowable and flexible material which can fill and conform to theinterior volume of the target location within the appliance trough.Optionally, an adhesive or other treating material will be coated on thetarget location prior to filling with the pontic material. The flowablepontic material will then be cured to form the final pontic. Optionally,the shape of the pontic can be modified using spatulas (while it isstill workable) and/or knives (after it has cured). Preferably, thepontic will be shaped so that it fills substantially the entire gapbetween adjacent teeth and extends down to the gingiva, withoutintruding upon the gingiva when the aligner or other appliance is worn.

In a specific embodiment of the present invention, curable siliconecompositions, especially the addition-curable silicone rubbercompositions known in the art are employed to form an elastomeric,flexible polyvinylsiloxane (PVS) dental pontic. Typically thesepolyvinylsiloxane materials are formed from a two component curablesilicone prepolymer system. A first component, which is referred to as a“Base Paste”, typically contains a vinylorganopolysiloxane dispersion,an organo hydrogen-polysiloxane, inorganic fillers and other additiveswell known in the art. The second component of this two-part compositionis referred to as a “Catalyst Paste” and typically consists of a secondportion of the vinyl polysiloxanes, polymerization initiators,accelerators, cross-linking agents and other additives well known in theart. The base and catalyst may either be hand mixed and delivered to theappliance trough using a spatula or application syringe or a mixingdevice such as an auto-mix cartridge commonly used for impressionmaterials may be employed to combine the proper volumes of base andcatalyst. The tip size of the nozzle can be selected to provide adesired ribbon of material to be delivered to the appliance trough.Preferably, the tip of the nozzle will be held beneath the surface ofthe PVS as it is being dispensed within the appliance trough. Byproviding applicators having different tip diameters, the size of thematerial ribbon and the pontic can be selected by the treatingphysician.

Another class of curable silicone rubbers useful in forming elastomericdental pontics are the condensation reaction silicones. Condensationsilicones are supplied as either a paste and liquid or as two pastes.Typically the base paste consists of a silicone polymer with terminalhydroxy groups and a filler and the catalyst paste consists of across-linking agent (organohydrogen siloxane) and an activator such asdibutyl-tin dilaurate. On mixing the two pastes react by a condensationreaction causing cross-linking. Typically the setting reaction producesa gas such as hydrogen or an alcohol.

Prior to delivering the curable silicone rubber, an adhesive is appliedto the aligner segment corresponding to the site of the missing tooth toenhance the bond between the PVS pontic and aligner thermoplastic.

After sufficient material has been dispensed to form the pontic, thetreating clinician may optionally shape or form the pontic as desired,typically using conventional shaping tools, such as spatulas. Thematerial will then be cured. In the case of PVS, curing will typicallyoccur after five to ten minutes at room temperature but anybody skilledin the art can vary the material composition to allow for curing times<60 seconds or as long as 24 hours. If it is desired to expedite curing,the PVS material may be gently warmed, e.g., held under a warm waterstream. After curing, shaping or trimming of the pontic may be performedusing a knife, abrasive instrument, or the like.

Non-toxic, inorganic iron oxide pigments may be incorporated in the PVSpolymer to provide for a tooth-colored shade for the finished pontic.Optionally, a range of tooth-colored PVS resins may be provided in a kitallowing the clinician to select a color that best matches patient'steeth. In a second aspect of the present invention, kits are providedcomprising components of the system useful for performing the methodsdescribed above. In particular, the basic kit would include a curable,toothshaded PVS resin material such as described above in combinationwith instructions for use setting forth a method for forming the ponticwithin the trough of an aligner or other thin polymeric appliance havinga trough or cavity which is removebly placed over teeth. In particular,the instructions will set forth a first step of determining the locationin the trough where a tooth is missing from the patient's dentition, anda second step comprising filling the location with the filler so thatthe material resembles a tooth when the location is filled.

Optionally, the kit may further include other components, such as anadhesive for coating an interior surface of the appliance trough at thelocation to be filled. When an adhesive is supplied, the kit willtypically also include a brush, sprayer, or other applicator forapplying the adhesive to the appliance trough. The kit may still furthercomprise one or more nozzles for use with a filler applicator fordispensing the curable filler material within the appliance trough.Typically, the filler applicator will be a dispensing gun capable ofapplying the PVS resin in a controlled manner through the nozzle whichis attached to the gun. More typically, the kit will include two or morenozzles, where each nozzle will have a different tip diameter todispense a different ribbon size of the filler to most efficiently filltarget locations of differing sizes. Further optionally, the kit mayinclude two or more cartridges or other containers of the curable fillermaterial, where the materials have different properties, such as color.Still further optionally, the kit could include one or more coloringmaterials to permit the clinician to mix and color the filler materialat the time of use. In addition, the kit may include one or more shapingtools which permit precise sizing and shaping of the pontic. Forexample, the kit may be provided with a spatula for sizing and shapingthe material before it is cured. Alternatively or additionally, the kitmay comprise a knife, grinder, or other tool for shaping and removingthe filler material after it has cured. To facilitate the fabrication ofdental pontics in a manufacturing setting, the curable tooth-coloredsilicone rubber catalyst- and base-paste may be supplied in foil bagsand precisely dispensed from a Pentamix system eliminating eitherhand-mixing or dispensing with a hand held dispensing gun.

In a third aspect of the present invention, improved methods forrepositioning teeth after extractions or impatience with substantialgaps between adjacent teeth are provided. The improvements are inmethods for repositioning teeth which use polymeric shell applianceseach of which have a trough for receiving and resiliently repositioningthe teeth, e.g., as in the Invisalign® System commercially availablefrom Align Technology, Inc., assignee of the present application. Thepolymeric shell appliances have different geometries and are wornsuccessively by a patient to reposition the teeth in a number of stages.The improvement comprises providing at least some of the polymeric shellappliances, also referred to as aligners, which have pontics at alocation within the appliance trough which will fill a gap between teethwhen the appliance is worn. Usually, each appliance worn will have apontic at the location of the gap, and the size of the pontic may bedecreased as the treatment progresses and the width of the gap closes.In addition to the esthetic benefits described above, the provision of apontic within the gap as the teeth are being closed is believed toprovide therapeutic benefits as well. In particular, the presence of thepontic will reduce or eliminate the tendency of teeth which are beingclosed over a gap to tilt or incline into the gap. Thus, it is expectedthat teeth which are treated with the polymeric appliances to close suchgaps will remain generally more upright as they are moved, thus reducingor eliminating the need to correct any tilt or inclination which isinduced by the treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an aligner of the type employed in the Invisalign®System being placed over a patient's teeth.

FIGS. 2A and 2B illustrate a portion of the aligner of FIG. 1 prior toplacement of a pontic (FIG. 2A) and after placement of a pontic (FIG.2B). For convenience, placement of the pontic is shown in black, but itwill be appreciated that in practice the pontic will usually be a shadeof white selected to match the patient's teeth.

FIG. 3A is a cross-sectional view taken along line 3A-3A of FIG. 2A,showing a view of the aligner prior to filling with the pontic material.

FIG. 3B illustrates filling of the aligner with the pontic material.

FIG. 3C is a cross-sectional view taken along line 3C-3C of FIG. 2B,showing the aligner after the pontic has been formed therein.

FIG. 4 illustrates a kit constructed in accordance with the principlesof the present invention.

FIG. 5 illustrates an exemplary process for generating an alignercapable of receiving the pontic material.

FIG. 6 shows an exemplary pontic in an aligner.

FIG. 7 shows an exemplary space filler in an aligner.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention provides improved methods and kits for the use ofaligners 100 for positioning teeth in a tooth arrangement TA, asillustrated in FIG. 1. The aligner is a thin shell polymeric applianceof the type commercially available as part of the Invisalign® Systemavailable from Align Technology, Inc., Santa Clara, Calif. The planningand fabrication of such aligners is described in detail in issued U.S.Pat. No. 5,975,893, the full disclosure of which has previously beenincorporated herein by reference. The aligners 100 are worn by a patientover the tooth arrangement for a sufficient time to rearrange the teethto a desired subsequent tooth arrangement. A plurality of successivealigners are worn until an entire course of the treatment is completed.

As shown in FIG. 2A, the aligner 100 will include a number of individualtooth- shaped segments 102, 104, 106, 108, and 110. Each of theseindividual segments will be designed to fit over an individual tooth,with the particular placement of the segment being moved slightly toeffect a corresponding tooth movement while the aligner is worn.

For the purposes of describing the present invention, it will be assumedthat the tooth corresponding to segment 108 will be extracted, e.g., toremove over-crowding. Once the tooth is removed, of course, there willbe a void or gap left between the teeth which are beneath segments 106and 110. The purpose of the present invention is to provide anartificial tooth, commonly referred to as a pontic, within the cavity ortrough of the aligner 100 which would have covered the tooth prior toextraction. The aligner 100 having a pontic formed in the interior ofsegment 108 is illustrated in FIG. 2B. For ease of illustration,presence of the pontic is shown by coloring the segment 108 black. Inactual practice, of course, the pontic will usually be colored a shadeof white to match the patient's other teeth.

Referring now to FIGS. 3A-3C, formation of a pontic 120 in the toothsegment 108 of aligner 100 will be illustrated. Initially, the trough112 of the tooth segment 108 is empty, as illustrated in FIG. 3A. Abonding agent is applied to the tooth aligner tooth trough asillustrated in FIG. 3B. The bonding agent may be a simple compound, morepreferably a polymer which attaches or substantively, adhesively,cohesively or otherwise bonds the curable silicon rubber to the alignerthermoplastic. The preferred bonding agents can be those disclosed inGerman Pat. DE 19934117 to Engelbrecht et al. The pontic is preferablyformed by dispensing a curable PVS prepolymer resin (M) as shown in FIG.3B. Typically, the curable PVS prepolymer resin will be dispensedthrough a mixing nozzle 114 from an applicator 115. The applicator canbe a conventional dispenser gun, e.g., holding a dual cartridge; onecartridge containing the uncured PVS resin base, inorganic fillers andother additives known in the art the other containing the catalystcomponents. As the trigger of the dispensing gun is squeezed, the PVSbase and catalyst materials flow through the mixing nozzle where theyare combined initiating the curing of the PVS rubber. The PVS rubber isdispensed through the mixing nozzle, where the width of the beaddispensed is determined by the tip diameter of the nozzle. Preferably,the tip diameter of the nozzle will be selected to provide anappropriate material bead size to fill the trough 112 at a desired rate.Useful tip diameters will be in the range from 0.01″ inches to 0.2″inches, preferably from 0.03″ inches to 0.10″ inches. The PVS rubberwill be dispensed, preferably while maintaining the nozzle tip beneaththe surface of the material, until the trough 112 is substantiallyfilled, as shown in FIG. 3C. At that point, the pontic 120 has beenformed. Immediately after dispensing the PVS rubber in the alignertrough the user may, if necessary, sculpt and contour the material usinga spatula or similar instrument. The user may continue to do this duringthe “working phase” of the resin curing process. Useful working phasetimes will be in the range from 30 seconds to 5 minutes, preferably from45 seconds to 3 minutes. Curing or hardening of the PVS filler materialwill then take an additional 3 minutes to 10 minutes depending on theformulation After the pontic material has cured, it may still be shapedusing a knife, abrasive instrument, or the like. In addition to fittingthe pontic so that it can be inserted and removed between the adjacentteeth, it is also desirable that the exposed portion of the pontic notintrude upon the gingiva. The treating clinician can place the aligner100 over the patient's teeth to make sure that it fits properly beforereleasing the aligner to the patient.

Referring now to FIG. 4, a kit 200 adapted for forming pontics withinaligners or other polymeric shell appliances will be described. The kit200 will include at least a container 202 which holds the ponticmaterial. Typically, the container 202 will be in the form of acartridge which may be dispensed through a conventional applicator, suchas a gun-type applicator used with the preferred PVS filler material.The kit 200 will also include instructions for use 204 which set forththe methods of the present invention, as generally described above.Optionally, the kit may further include one or more nozzles 114 whichmay be used together with the applicator, as generally described above.In preferred embodiments, the kits will include two or more nozzles,where the nozzles have different tip diameters to permit dispensing ofdifferent bead sizes of the filler material into the aligner. Furtheroptionally, the kit may include a bonding agent, as described in GermanPatent DE 19934117 assigned to Engelbrecht et al. for coating theinterior of the aligner prior to dispensing of the pontic material. Whenincluding the adhesive 206, a brush 208 may also be provided eitherseparately or optionally within the cap of the adhesive container. Othertools, such as a spatula 210 for forming the filler material prior tohardening, a knife or other tool for forming the pontic material afterhardening, and the like, may also be provided. Preferably, allcomponents of the kit will be packaged together with a box, tray, pouch,tube, or other conventional medical device package 220.

FIG. 5 illustrates an exemplary process 500 for generating an alignercapable of receiving the pontic material. The process of FIG. 5 createsa pontic that is customized to each patient. The customization is neededsince shapes of teeth vary: for the same tooth, different patients havedifferent tooth sizes and shapes. In order to represent a generic toothshape that can be modified for each patient, a standard parametric toothmodel is employed, and the process 500 customizes the parametric toothmodel to each patient.

Starting from the first tooth position that requires a pontic, theprocess 500 determines a tooth identification or tooth type (step 502).Next, the process 500 determines neighboring teeth dimensions (step504). The parameters are determined by the neighboring teeth dimensions.The height of the pontic is determined in proportion to the neighboringteeth heights. The pontic thickness is also proportional to theneighboring teeth thickness. Other parameters can be predefined orproportional to the neighboring teeth.

The process 500 then determines the gap size based on the neighboringteeth dimensions as the pontic width also depends on the gap size (step506). Next, the process 500 determines whether the gap providessufficient clearance for the pontic (step 508). From step 508, if thegap is too small, the process exits (step 520). Alternatively, if thegap is sufficient, the process 500 determines the pontic parameters(step 510). It also determines the pontic position (step 512). Theprocess 500 also creates pontic geometry for the current tooth (step514). Step 514 completes the processing for the current tooth, and thenext tooth for the current stage is selected (step 516) before theprocess loops back to step 508. The pontic is updated in each stage,thus each stage has a different pontic. Thus, the pontic will be updatedas the stage changes.

FIG. 6 shows an exemplary pontic 600 in an aligner. The position of thepontic 600 is determined by the neighboring teeth 602 and 604. As shownin FIG. 6, two points 610 and 612 on the interproximal area of theneighboring teeth are used to define an axis 620. The pontic 600 isplaced in contact with a plane that passes the two points 610 and 612.The position can be manually adjusted by the user.

FIG. 7 shows an exemplary space filler 700 between two teeth 702 and 704in an aligner. The space filler 700 is used when the missing tooth is inthe posterior region of the jaw that is not likely to be visible. Insuch situation, a geometric beam is formed connecting the center of theteeth 702 and 704 and the beam width is selected that is smaller thanthe diameters of the teeth 702 and 704 and a geometric filling isperformed to fill in the beam. The use of the space filler 700 providesstructural strength to the resulting aligner while avoiding the costsassociated with a pontic.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

1. An improved method for repositioning teeth using polymeric shellappliances which each have a trough to receive and resilientlyreposition teeth, wherein the appliances have different geometries andare worn successively by a patient to reposition teeth, wherein theimprovement comprises providing a pontic at a location in at least oneof the appliance troughs to fill a gap between teeth when the applianceis worn.
 2. An improved method as in claim 1, wherein the improvementfurther comprises providing a pontic at a location in at least oneadditional of the appliance troughs to fill the gap between teeth whenthe additional appliance is worn.
 3. An improved method as in claim 2,wherein the gap is being closed as the teeth are repositioned, whereinthe size of the pontic is reduced in successive appliances.
 4. Animproved method as in claim 3, wherein presence of the pontic when theappliance is worn inhibits collapse of adjacent teeth into the gap asthe adjacent teeth are moved together to close the gap.